A micro electro mechanical system (MEMS) is configured by integrating a mechanical element, a sensor, an actuator, an electronic circuit and the like on the same substrate. The MEMS is utilized in a variety of fields such as a printer head and a pressure sensor.
Meanwhile, when the MEMS is used as a high-frequency device, there are a cold switching and a hot switching as a method for turning on and off a high-frequency signal transmitted via a signal line. The cold switching is a method for making a signal line on a ground line move up and down with the signal line receiving no high-frequency signal, while the hot switching is a method for making a signal line on a ground line move up and down with the signal line receiving a high-frequency signal.
In the hot switching, a self-holding phenomenon occurs when a signal line is made to transition from a down state to an up state. That is, in the hot switching, an electrostatic attraction is generated by the high-frequency signal, whereby the signal line is held in the down state independently of the drive signal which makes the signal line move up or down.
In order to avoid such a self-holding phenomenon, a spring constant of a support member supporting the signal line is increased so as to make the signal line transition from a down state to an up state against the electrostatic attraction generated by the high-frequency signal.
Meanwhile, for example, Japanese Patent Application Publication No. 2008-145440 discloses a method for setting a potential different from a potential of a size mass by providing an auxiliary electrode outside an electrode forming a capacitor in order to reduce an impact of the fluctuating surface load on an output signal of an inertial sensor of a micromachine structure.
However, when the spring constant of the support member supporting the signal line is increased to avoid the self-holding phenomenon, a drive voltage for making the signal line transition from an up state to a down state may be increased.
According to the method disclosed by Japanese Patent Application Publication No. 2008-145440, since the signal line and the ground line are placed facing each other, the electrostatic attraction depends on a gap between the signal line and the ground line. For this reason, the electrostatic attraction between the signal line and the ground line increases, and the size of the auxiliary electrode may be accordingly increased. This may cause a problem of increasing the parasitic capacitance between the signal line and the ground line.